Sedimentological analysis of ash-rich pyroclastic density currents, with special emphasis on sin-depositional erosion and clast incorporation: The Brown Tuff eruptions (Vulcano, Italy)

The sedimentological, lithological and textural characteristics of the Brown Tuffs (BT) pyroclastic deposits, combined with their grain-size, componentry geochemical glass compositions, are here investigated to obtain information on transport depositional mechanisms corresponding density currents (PDCs). BT widespread reddish-brown grey, ash-rich deposits generated by pulsating hydromagmatic explosive activity from La Fossa Caldera Vulcano island during c. 80–6 ka time-stratigraphic interval, then distributed most Aeolian Islands Capo Milazzo peninsula (Sicily) in Tyrrhenian Adriatic Sea regions. Near source area Vulcano, characterised alternating massive planar cross stratified lithofacies that result stepwise, repeating aggradation discrete PDC pulses. This alternance is regulated either fluid escape or granular flow regimes at high clast concentration grain traction deposition waning diluted stages PDCs. Most show intermittently ash resulting a pervasive post-depositional disruption primary structures. induced upward expulsion associated dissipation pore pressure between layers different size (fine coarse ash) porosity, as outlined distinctive upwards bends pillar-type structures through fluid-filled cracks rupture points. Massive faint colour grain-size banding widely recognised Lipari, nearby Vulcano. Based presence, base units, cm-thick amalgamation bands containing pumice lapilli, scoria lithic clasts ripped-up embedded loose underlying they interpreted deposited PDCs laterally spreading moving Lipari. During motion Lipari these (likely) crossed narrow shallow sea-water inlet which did not stop advancement but influenced distribution those mainland. In this paper, mechanism erosion incorporation across whole means field study, analyses components mixed basal BT. suggests maintained enough power erode substratum, hence likely impacting territory, over distance up least 16–17 km volcanic source. Evidence exerted shear-stress substratum also provided undulated, recumbent flame rip-up some units southern central order form such bed instabilities we calculate had shear velocity ca. 2 m s−1 stress range 1‐4.5 kPa. These results add new insights large-scale hazard shed lights dynamics flows sea reaching islands, interactions pre-depositional topography.